Clarify stage3_debug rewrite-first behavior in quickstart docs

SESSION_QUICKSTART.md

@@ -69,7 +69,7 @@ ls -la data/eval_results/
 - **Add category**: Edit `tagging_checklist.txt`, update parser
 - **Eval changes**: Run `scripts/eval_pipeline.py`, then `scripts/eval_categorized.py`
 - **Test retrieval**: Use `scripts/smoke_test.py`
-- **Debug Stage 3**: Use `scripts/stage3_debug.py`
+- **Debug Stage 3**: Use `scripts/stage3_debug.py` (`--phrases` optional; omitted runs Stage 1 rewrite first, then Stage 2 retrieval from rewritten phrases)
 
 ## Data Artifacts (Lazy-loaded)
 - FastText embeddings (semantic similarity)